WIKA Equips Syngas Plant with Long-Lasting Thermocouples

At a Texas-based syngas plant, the thermocouples in its partial oxidation units were lasting an average of three months before failing. But after switching to WIKA’s TC84 platinum thermocouple with sapphire protection tube, the facility has not had to replace its temperature sensors for over a year.
 

Problem: Syngas Plant Experiences Repeated Instrument Failures

A multinational chemical company has a plant that produces syngas through the partial oxidation of a feedstock using pure oxygen. This hydrocarbon feed consists of:

• Methane: ~85–98%
• Tail gas (from an adjacent ethylene facility): ~0–10%
• Acetylene off gas (from a nearby acetylene facility): ~0–5%
• Liquid hydrocarbon (from an adjacent methanol facility): ~0–5%

The natural gas portion of the feedstock is pretreated in catalyst beds to remove much of its sulfur before entering the thermal POX reactor. After partial oxidation, the resulting crude syngas has an average composition of:

• 60% H₂
• 30% CO
• ≤5% CO₂
• Water and trace amounts of unreacted CH₄

The average temperature of the process gas is 1400°C (2552°F) around 70 bar (1015 psi). As most thermocouples are unable to tolerate temperatures past 1200°C (2192°F), nor are they protected from hydrogen embrittlement, the syngas plant was experiencing repeated instrument failures where the sensors in the TPOX reactor would melt, crack, or break after only an average of three months of use. They needed a more durable and longer-lasting thermocouple.

WIKA’s Solution: TC84 Thermocouple with Patented Sapphire Design

After a thorough analysis of the plant’s processes, WIKA proposed a solution: the TC84 sapphire-design thermocouple. This high-temperature temperature sensor with a gas-tight sapphire protection tube has a monocrystalline structure that shields the thermocouple’s sensitive wires from hydrogen permeation and temperatures as high as 1700°C (3092°F). The device has a primary seal, with a secondary seal offering backup protection.

The TC84 comes in two versions, both with a solid-machined safety chamber and ceramic outer protection tube.

• For processes with little or no hydrogen content, the measuring insert is also a ceramic protection tube.
• For processes with a high hydrogen content, the measuring insert is a sapphire protection tube.

WIKA recommended the version with the sapphire protection tube as the plant’s process gas has a high H₂ content.

After a visit to WIKA’s R&D Center for Temperature Measurement in Houston, the chemical company was impressed by their expertise and capabilities, and agreed to a trial run. They replaced all six thermocouples in one partial oxidation reactor with TC84s of various lengths, inserted horizontally using a flange connection. After nine months where no thermocouples failed, the happy customer decided to standardize and replace all the thermocouples in the other three POX units with WIKA’s thermocouple with sapphire protection tube.

With the TC84, this partial oxidation plant was able to:

• Save money and time by not having to replace sensors every three months. As of publication time, the TC84 has been in service for over 12 months.
• Repair rather replace worn sensors, when the time comes.
• Minimize maintenance by eliminating the need for a purge system.
• Increase production by minimizing the number of outages due to inaccurate instrumentation data.
• Increase operational flexibility with minimum failures due to repeated heat cycles.

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